1. Technical Field
The present invention relates to a jitter measurement apparatus, an electronic device and a test apparatus. More particularly, the present invention relates to a jitter measurement apparatus which adjusts a measurement gain.
2. Related Art
A jitter measurement apparatus is, for example, a device for converting jitter of a signal under measurement which is measured on the time axis into a voltage signal, and outputting the voltage signal. Here, the amount of jitter (variation in timing) of the signal under measurement is converted into the amount of voltage by using a conversion coefficient (a jitter gain) which is uniquely assigned to the jitter measurement apparatus. Considering this, the jitter gain of the jitter measurement apparatus is preferably known. If the jitter gain is known, the amount of jitter which is measured on the time axis can be obtained by dividing the voltage value output from the jitter measurement apparatus by the jitter gain.
The jitter gain of the jitter measurement apparatus can be obtained, for example, by using the following method. Before the signal under measurement is measured, a known amount of jitter is injected into a reference signal, the reference signal is then input into the jitter measurement apparatus, and the voltage value output from the jitter measurement apparatus is measured. The jitter gain of the jitter measurement apparatus can be estimated in advance based on the ratio between the measured voltage value and the known jitter amount.
However, if the jitter measurement apparatus is affected by PVT (process, voltage, temperature) variations while measuring the signal under measurement, the operational characteristics of the elements of the jitter measurement apparatus dynamically change. As a result, the jitter gain which is used for the measurement of the signal under measurement may be different from the jitter gain which is estimated before the measurement of the signal under measurement.
Furthermore, if a reference signal having a high frequency is input into the jitter measurement apparatus, the reference signal is degraded by, for example, the LC component of the transmission path from the outside of the jitter measurement apparatus to the measuring circuit disposed inside the jitter measurement apparatus. Such degradation causes a change in the known jitter amount of the reference signal input into the jitter measurement apparatus, thereby making it difficult to estimate an accurate jitter gain of the jitter measurement apparatus.
Since it is difficult to accurately estimate the jitter gain of the jitter measurement apparatus as discussed above, the jitter amount of the signal under measurement can not be accurately measured.
In view of the foregoing description, an advantage of some embodiments of the present invention is to provide a jitter measurement apparatus, an electronic device and a test apparatus which can solve the above-mentioned problems. This advantage is achieved by combining the features recited in the independent claims. The dependent claims define further effective specific example of the present invention.